ARLETE SIMÕES BARNEZE
N2O emission from soil due to urine deposition by grazing cattle
and potential mitigation
N
2O emission from soil due to urine deposition by grazing cattle
and potential mitigation
Reviewed version according to the “Resolução CoPGr 6018 de 2011”
Dissertation presented to Centro de Energia Nuclear na Agricultura da Universidade de Sao Paulo as a requisite to the MS Degree in the Sciences
Concentration Area: Chemistry Applied to Agriculture and the Environment
Advisor: Prof. Dr. Carlos Clemente Cerri
AUTORIZO A DIVULGAÇÃO TOTAL OU PARCIAL DESTE TRABALHO, POR QUALQUER MEIO CONVENCIONAL OU ELETRÔNICO, PARA FINS DE ESTUDO E PESQUISA, DESDE QUE CITADA A FONTE.
Dados Internacionais de Catalogação na Publicação (CIP)
Seção Técnica de Biblioteca - CENA/USP
Barneze, Arlete Simões
Emissão de N2O do solo devido à aplicação de urina e o potencial de mitigação / N2O emission from soil due to urine deposition by grazing cattle and potential mitigation / Arlete Simões Barneze; orientador Carlos Clemente Cerri. -versão revisada de acordo com a Resolução CoPGr 6018 de 2011. - - Piracicaba, 2013.
87 f.: il.
Dissertação (Mestrado – Programa de Pós-Graduação em Ciências. Área de Concentração: Química na Agricultura e no Ambiente) –Centro de Energia Nuclear na Agricultura da Universidade de São Paulo.
1. Efeito estufa 2. Fluxo dos gases 3. Inibidores químicos 4. Nitrificação 5. Nitrogênio 6. Óxido nitroso 7. Pecuária 8. Temperatura do solo 9. Umidade do solo 10. Uréia I. Título
To my honorable parents, Cilene and Wanderlei, and my adorable brother, Vítor, who always were and still are a solid basis of my entire life.
And to my boyfriend, Caio, for the essential companionship, for the patience, for true love and for all the support necessary to complete this step.
Aos meus digníssimos pais, Cilene e Wanderlei, e ao meu adorável irmão, Vítor, que sempre foram e continuam sendo o alicerce concreto da minha vida.
E ao meu namorado, Caio, pelo imprescindível companheirismo, paciência, grande amor e apoio fundamentais para a finalização dessa etapa.
ACKNOWLEDGMENTS
A dissertation is a result of a series of challenges, difficulties, uncertainties, and why not achievements and winnings. It can only be achieved with motivation, determination and enthusiasm that we look for inside ourselves and acquire from loved scientific or personally ones who encourage to continue and give the necessary support.
These people were essential to complete this dissertation, and I've been come through this to exalt my sincere and humble acknowledgments.
First, I thank God, who was always by my side, became very present in my life in many moments.
"Be strong and with courage; do not amaze, nor be dismayed, for the Lord your God is with you wherever you go" (Josué 1:9).
I thank my parents and my brother, who is the inspiration of my life, have always been with me, supporting and encouraging me, and understanding many times I've been absent, but always with them inside my heart.
My sincere gratitude to Prof. Dr. Carlos Clemente Cerri for his guidance and encouragement provided since the beginning of the research. Thank you to trust me and to give me opportunities for my scientific and personal development.
I am very grateful to irrefutable Dr. Tom Misselbrook for the excellent supervision, patience, friendship and valuable suggestions in this research.
Thank the Centre of Nuclear Energy on Agriculture for the opportunity to taking my cours.
My gratitude to the excellent institute of Rothamsted Research, North W yke in England for the opportunity to do the research, to promote the availability of materials and structure necessary to achieve this exchange of knowledge.
To São Paulo Research Foundation for the scholarship, overseas internship´s scholarship and financial support to the project.
To my friends in Rothamsted Research, in special to the renowned researcher Laura Cardenas, and Alison Moxey, Andy Retter, Cristina Alcántara, Don Harkness, Gary Egan, Mark Tooth, Neil Donovan, Rebecca Murray e Stuart Norris for the cooperation in the experiments, for the encourage the English’s learning and from all the true friendship and relaxed moments.
To everyone who directly and indirectly contributed to this work.
AGRADECIMENTOS
A finalização de uma dissertação é fruto de uma série de desafios, dentre eles, dificuldades, incertezas, tropeços e, porque não, conquistas e vitórias. Esta só é possível de ser concretizada com estímulo, força de vontade e muito entusiasmo que buscamos dentro de nós mesmos e que absorvemos de pessoas queridas que científica ou pessoalmente aproximam-se de nós, nos encorajando a continuar e nos dando o respaldo necessário.
Para mim essas pessoas foram essenciais na elaboração desta dissertação, e venho por meio destes exaltar os meus sinceros e humildes agradecimentos.
Primeiramente, agradeço a Deus, que além de estar ao meu lado sempre, se fez muito presente na minha vida em diversos momentos delicados, não me deixando esmorecer.
“Esforça-te, e tem bom ânimo; não pasmes, nem te espantes, porque o Senhor, teu Deus, é contigo, por onde quer que andares” (Josué 1:9).
Aos meus pais e meu irmão, que são minhas inspirações na vida, estiveram sempre comigo, me apoiando e incentivando, e acima de tudo compreendendo as muitas vezes que estive ausente, mas sempre com eles no coração.
Ao meu querido orientador, Dr. Carlos Clemente Cerri, pela orientação e grande incentivo proporcionado desde o início. Agradeço-lhe por ter confiado em mim e concedido diversas oportunidades para meu desenvolvimento científico e pessoal, além da amizade construída.
Aos professores Adibe Luiz Abdalla, Brigitte Josefine Feigl, Carlos Eduardo Pellegrino Cerri e Quirijin de Jong van Lier, pela amizade e ensinamentos durante todas as etapas da pesquisa.
Ao inestimável Dr. Tom Misselbrook pela excelente supervisão, demasiada paciência, grande amizade e irretocáveis sugestões para a concretização desta pesquisa.
Ao Centro de Energia Nuclear na Agricultura pela formação profissional, acadêmica e pessoal.
Ao Departamento de Zootecnia da ESALQ/USP e ao Prof. Dr. Luiz Gustavo Nussio pela disponibilização de estrutura para o desenvolvimento da pesquisa.
Ao Rothamsted Research, North W yke na Inglaterra pela oportunidade de pesquisa, promovendo a disponibilização de materiais e estrutura necessária para a realização desse intercâmbio de conhecimentos.
À Fundação de Amparo à Pesquisa do Estado de São Paulo pela concessão da bolsa de mestrado, e de estágio no exterior e pelo apoio financeiro ao projeto.
Aos funcionários do Laboratório de Biogeoquímica Ambiental do CENA/USP Admilson R. Margato, Dagmar G. M. Vasca, Lilian A. C. Duarte, Ralf V. de Araújo, Sandra M. G. Nicolete e José V. de Souto pelo auxílio nas análises, apoio na execução do projeto e pela amizade.
À Marilia Henyei pelas preciosas correções na elaboração deste trabalho.
execução dos experimentos e pela grande amizade construída. À querida Jaqueline Bueno de Campos que foi mais que uma estagiária; agradeço pela intensa colaboração no desenvolvimento e análises do experimento, além da sincera amizade. Ao Marcos Siqueira Neto pelas numerosas sugestões para o desenvolvimento da pesquisa. E ao João Antonio Braga Rocha pela intensa colaboração no trabalho e pela amizade.
Aos colegas do Rothamsted Research em North W yke, em especial à pesquisadora Laura Cardenas e aos demais amigos Alison Moxey, Andy Retter, Cristina Alcántara, Don Harkness, Gary Egan, Mark Tooth, Neil Donovan, Rebecca Murray e Stuart Norris, pela colaboração nos experimentos, pelo incentivo na aprendizagem do inglês e acima de tudo pela amizade e momentos de descontração.
Às minhas queridas amigas Adriana Marcela Silva Olaya, Alice de Sousa Cassetari, Ana Cláudia Lo Buono Tavares, Natália Rocha, Ingrid Helen Grígolo e Taís Siqueira que estiveram comigo sempre.
E a todos que, direta e indiretamente, contribuíram para a realização deste trabalho.
“All our dreams can come true, if we have the courage to pursue them”
ABSTRACT
BARNEZE, A. S. N2O emission from soil due to urine deposition by grazing
cattle and potential mitigation. 2013. 87 p. Dissertation (M.S.) –Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Piracicaba, 2013.
Grazing pasture is a major system of livestock production in many countries and it has been identified as an important source of N2O from urine deposition on soils. The
aim of this study was to determinate the N2O emissions from soil after urine
deposition and the emission factor, in addition, determine how temperature and water content of the soil influence these emissions. We also intended to study a potential of mitigation using nitrification inhibitors. Soil and gas samples were collected in traditional livestock areas in Brazil and UK to evaluate the N2O emission dynamics
under field conditions. In addition, incubation experiments were conducted to evaluate how temperature and water content affect N2O emissions in the soil and to
study the potential mitigation on N2O emission from the soil after urine application,
using two distinct nitrification inhibitors. In the field experiment, the N2O emission
factor for cattle urine was 0.20% of the applied urine N in Brazil and 0.66% for the UK conditions. The incubation experiments showed the N2O emissions after urine
application are higher in soils with high moisture and high temperature. The nitrification inhibitor effectiveness was not statistically significant, however had shown some N2O emission absolute reductions among 6% to 33% comparing with urine
only application on the soil. Various physical and biological factors can be influence the effectiveness of the products. It confirmed that urine deposition can contribute to N2O emission from the soil and the temperature and water content can markedly
increase these emissions. The nitrification inhibitors have a potential mitigation effect since some decreased emissions of almost 40%. The results in this study are pioneers and can be used as a basis for more complex evaluations and to help with determining the carbon footprint of beef production worldwide.
RESUMO
BARNEZE, A. S. Emissão de N2O do solo devido à aplicação de urina e o
potencial de mitigação. 2013. 87 p. Dissertação (Mestrado) – Centro de Energia Nuclear na Agricultura, Universidade de São Paulo, Piracicaba, 2013.
Considerado o maior sistema de produção animal em muitos países, as pastagens tem sido identificadas como uma importante fonte de emissão de N2O, devido à
deposição de urina ao solo. O objetivo deste estudo foi determinar as emissões de N2O do solo após a deposição de urina e seu fator de emissão, além disso,
determinar como temperatura e teor de água do solo influenciam as emissões. Pretendeu-se também estudar o potencial de mitigação das emissões de N2O
usando inibidores de nitrificação. Amostras de solo e de gás foram coletadas em áreas tradicionais de pastagens do Brasil e do Reino Unido para avaliar a dinâmica das emissões de N2O. Experimentos de incubação também foram realizados para
avaliar a influência de fatores como temperatura e teor de água no solo nas emissões, além de avaliar o potencial de redução das emissões de N2O do solo
após a aplicação da urina, utilizando dois inibidores de nitrificação. Nos experimentos de campo realizados no Brasil e no Reino Unido, o fator de emissão do N2O para a urina foi de 0,20% e 0,66% do nitrogênio na forma de urina bovina
aplicada, respectivamente. Nos experimentos de incubação, as emissões de N2O
após a aplicação de urina foram maiores em solos com alta umidade e alta temperatura. A eficácia no uso dos inibidores de nitrificação não foi estatisticamente significativa, no entanto mostrou uma redução absoluta entre 6% a 33% nas emissões de N2O comparado com a aplicação de apenas urina ao solo. Vários
fatores físicos e biológicos podem ter influenciado a eficácia dos produtos. Dessa forma, confirma-se que a deposição de urina pode contribuir para a emissão de N2O
do solo e que a temperatura e o teor de água no solo podem aumentar consideravelmente essas emissões. Os inibidores de nitrificação podem ser usados como um potencial de mitigação, já que houve redução em termos absolutos de quase 40% nas emissões. Os resultados encontrados neste estudo são pioneiros e poderão ser utilizados como base para avaliações mais complexas e contribuir para a determinação da pegada de carbono na produção de carne mundial.
SUMMARY
1 INTRODUCTION ...19
2. LITERATURE REVIEW ...22
2.1 Greenhouse effect and climate change ...22
2.2 The nitrous oxide ...22
2.3 The importance of livestock on greenhouse gas emission ...24
2.4 Potential mitigation: the nitrification inhibitors...26
3 NITROUS OXIDE EMISSIONS FROM SOIL DUE TO URINE DEPOSITION BY GRAZING CATTLE IN BRAZIL ...33
Abstract ...33
3.1 Introduction...34
3.2 Material and methods ...35
3.2.1 Experimental site ...35
3.2.2 Urine characteristics ...35
3.2.3 Nitrous oxide measurement...36
3.2.4 Derivation of an emission factor ...37
3.2.5 Statistical analysis ...38
3.3 Results and discussion...38
3.3.1 Climatic conditions and nitrous oxide emissions ...38
3.4 Conclusions...41
References ...42
4 NITROUS OXIDE EMISSIONS AND SOIL NITROGEN DYNAMICS DUE TO SOIL MOISTURE CONTENTS AND TEMPERATURES ...45
Abstract ...45
4.1 Introduction...46
4.2 Materials and methods ...47
4.2.1 Soil and urine samples ...47
4.2.2 Experimental design ...47
4.2.3 Soil mineral N content ...48
4.2.4 Measurement of N2O emissions ...48
4.2.5 Statistical analysis ...49
4.3.1 Soil mineral nitrogen content ... 49
4.3.2 N2O emissions from the soil... 50
4.3.3 Cumulative emissions ... 50
4.5 Conclusions ... 56
References ... 56
5 NITROUS OXIDE EMISSIONS FROM THE SOIL FOLLOW ING CATTLE URINE APPLICATION: THE EFFECT OF NITRIFICATION INHIBITORS ... 61
Abstract... 61
5.1 Introduction ... 62
5.2 Material and methods ... 64
5.2.1 Laboratory experiment... 64
5.2.1.1 Experimental design ... 64
5.2.1.2 Experimental set up ... 65
5.2.1.3 Nitrous oxide measurement ... 65
5.2.1.4 Soil mineral N... 66
5.2.1.5 Statistical analyses ... 67
5.2.2 Field experiment ... 67
5.2.2.1 Site description ... 67
5.2.2.2 Experimental design ... 68
5.2.2.3 Nitrous oxide measurement ... 69
5.2.2.4 Soil mineral N... 69
5.2.2.5 Yields and N analysis from pasture... 69
5.2.2.6 Statistical analyses ... 70
5.3 Results... 70
5.3.1 Laboratory incubation ... 70
5.3.1.1 Nitrous oxide emissions ... 70
5.3.1.2 Cumulative emissions ... 71
5.3.1.3 Soil mineral N... 72
5.3.1.4 DCD degradation ... 73
5.3.2 Field experiment ... 73
5.3.2.1 Nitrous oxide emissions ... 73
5.3.2.3 Soil mineral N ...75
5.3.2.4 DCD degradation...76
5.3.2.5 Herbage yield and N offtake ...77
5.4 Discussion...78
5.4.1 N2O flux dynamics ...78
5.4.2 Effectiveness of NI...80
5.4.3 PDM and N uptake ...80
5.5 Conclusions...81
References ...81
1 INTRODUCTION
Recently one of world´s most concern is related to environmental impacts. Greenhouse gas emissions (GHG) are on the top of studied problems and their mitigation is a major challenge to modern society. Countries with reduction targets have developed studies to understand the processes and reduce emissions. These issues will become more important as nations align themselves with international agreements and policies to reduce environmental impacts.
Life cycle inventories are derived from indicators of environmental impact dealing with the potential effects on humans, environmental health and resources (SAUR, 1997). The carbon footprint has become the most important environmental protection indicator over the last few years (WIEDMANN; MINX, 2008; LAM et al., 2010). It usually stands for the amount of carbon dioxide (CO2) and other greenhouse
gases (converted to CO2-equivalent) emitted over the full life cycle of a process or
product. In that way, it is important to know the effect of each gas on the whole life cycle.
Agriculture releases to the atmosphere significant amounts of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) (COLE et al., 1997; IPCC, 2001;
PAUSTIAN et al., 2004). The most important practices include cropland management, grazing land management/pasture improvement, management of agricultural organic soils, livestock management and manure/bio-solid management. Their contribution is about 58% of total anthropogenic N2O emissions, with a wide
range of uncertainty in the estimates of both the agricultural contribution and the anthropogenic total (IPCC, 2007).
Grazing pasture is the main system of livestock production in many countries and it has been identified as an important source of N2O from urine deposition on
soils. Extensive management cause a substantial impact due to the large number of animals that such systems support, although it is characterized with low grazing intensity (1 head-1 ha-1 year-1 – Brazilian average) (FERRAZ; FELICIO, 2010) distributed in an abundant grazing land in the Cerradosregion.
Nitrous oxide is the third most important anthropogenic GHG with a global warming potential 298 times that of CO2 (IPCC, 2007). Besides that, the continuous
concern. An increase in N2O emission by 35-60% up to 2030 is expected due to
increases in nitrogen (N) fertilizer use and animal manure production (FAO, 2003). Adequate mitigation of these emissions is only possible if we understand the processes of N2O production. In view of this, the goal of this study was to determine
the specific emission factor for tropical conditions, understand the process and the factors that affect it, including the investigation of strategies to mitigate the emissions.
Initially, one pasture area in Southeast region of Brazil was chosen to provide some of the first data relating N2O emissions to urine deposition by grazing cattle in
Brazil (Chapter 3). After that, an experiment under controlled conditions was set up to determinate the effects of temperature and water content on N2O emissions and on
mineral N dynamics in the soil (Chapter 4). Field and incubation experiments were conducted in United Kingdom to evaluate the N2O emissions after urine application
with or without nitrification inhibitor, a potential mitigation option (Chapter 5).
This insight about N2O emission after urine deposition provides valuable
information to improve the knowledge about the emission from grazing system. This information can be used to calculate the carbon footprint of beef production and to incentive the research on mitigation strategies.
References
COLE, C. V.; DUXBURY, J.; FRENEY, J.; HEINEMEYER, O.; MINAMI, K.; MOSIER, A.; PAUSTIAN, K.; ROSENBERG, N.; SAMPSON, N.; SAUERBECK, D.; ZHAO, Q. Global estimates of potential mitigation of greenhouse gas emissions by agriculture. Nutrient Cycling in Agroecosystems, Heidelberg, v. 49, p. 221-228, 1997.
FAO. World Agriculture: Towards 2015/2030. An FAO perspective. FAO, Rome, 2003. 97 p.
FERRAZ, J.B.S.; FELÍCIO, P.E. Production systems: an example from Brazil. Meat Science, Loughborough, v. 84, p. 238-243, 2010.
IPCC. Climate Change 2001: the scientific basis. Contribution of Working Group I to the Third Assessment Report of the Intergovernmental Panel on Climate Change. [Houghton, J.T.; Ding, Y.; Griggs, D.J.; Noguer, M.; van der Linden, P.J.; Dai, X.; Maskell, K.; Johnson, C.A. (Ed.)]. Cambridge: Cambridge University Press, 2001. 881 p.
on Climate Change [Parry, M.L.; Canziani, O.F.; J.P Palutikof, P.J. van der Linden, C.E. Hanson (eds.)]. Cambridge: Cambridge University Press, 2007.
LAM, H. L.; VARBANOV, P.; KLEMEŠ, J. Minimising carbon footprint of regional
biomass supply chains. Resources, Conservation and Recycling, Amsterdam, v. 54, p. 303-309, 2010.
PAUSTIAN, K.; BABCOCK, B. A.; HATFIELD, J.; LAL, R.; MCCARL, B. A.; MCLAUGHLIN, S.; MOSIER, A.; RICE, C.; ROBERTSON, G. P.; ROSENBERG, N.
J.; ROSENZWEIG, C.; SCHLESINGER, W . H.; ZILBERMAN, D. Agricultural
mitigation of greenhouse gases: science and policy options. Ames, Iowa: CAST Council on Agricultural Science and Technology, 2004. 120 p. (CAST Report, R141).
SAUR, K. Life cycle impact assessment. International Journal of Life Cycle Assessment, Berlin, v. 2, n. 2, p. 66-70, 1997.
2. LITERATURE REVIEW
2.1 Greenhouse effect and climate change
The atmosphere and land surface are kept heated by energy from the sun in the form of ultra-violet, visible and infrared radiation. The ultra-violet radiation, in the stratosphere is intercepted by gas molecules such as diatomic oxygen and ozone and only a fraction of this energy reaches the earth. Fifty percent of incident energy is absorbed by the Earth´s surface; other 20% are absorbed by the gas phase and water droplets in the air. The remaining 30% are reflected back into space by reflective bodies. To keep the earth temperature constant, the amount of energy that the planet absorbs and releases must be the same. Some gases present in the air can temporarily absorb thermal infrared light, hence that not all energy released from the earth escapes into space. The light absorbed by these gas molecules is re-emitted in all directions randomly, resulting in energy reabsorption and causing an additional warming of the earth's surface and the air. This phenomenon is known as the greenhouse effect and is responsible for the average surface temperature at the middle ground to be between 15°C and 18°C (BAIRD, 2002).
Over the last century, the increase of trace gases concentration in the atmosphere is intensifying the natural greenhouse effect in about 0.74°C (IPCC, 2007). The main greenhouse gases are CO2, CH4, N2O, water vapour (H2O), ozone
(O3) and chlorofluorocarbons (CFCs). They reach the atmosphere mainly due to
anthropogenic activities, either directly by increased use of fossil fuels, industrial pollution and fires, or indirectly by irrational use of natural resources and also by agriculture, in many cases, practiced in an unsustainable way.
2.2 The nitrous oxide
Nitrous oxide is well known as “laughing gas”, despite it is becoming a highly
dangerous gas. N2O emissions have been and still are steadily rising since the start
Nitrous oxide is produced through several processes in the N cycle, related to the cycling of reactive N. It mainly may be emitted by nitrification and subsequent denitrification of the formed NO3-.
Microorganisms can break down organic N to (inorganic) ammonium (NH4+)
through mineralization. In this step the organic N become available for plants and microorganisms. Microorganisms can take up NH4+and convert it to nitrite (NO2-) and
nitrate (NO3-) by nitrification. Through denitrification, microorganism turns NO3- again
to (gaseous) N2(KNOWLES, 1982; ZUMFT, 1997).
These processes may occur simultaneously in different microsites of the same soil (STEVENS et al., 1997), but there is often uncertainty associated with which process is predominantly contributing to emissions.
N2O production from urine occurs only under specific conditions combining
aerobic and anaerobic processes, in other words, nitrification and denitrification, respectively. Recently it is increasingly been suggested that nitrifer denitrification (denitrification by autotrophic nitrifiers) may constitute a considerable contribution to N2O production in soil (WRAGE et al., 2004; MA et al., 2007). Although the N2O
production by nitrification is possible, the N2O emission peaks in soils are generally
attributed to the denitrification process (WRAGE et al., 2001; LEE et al., 2006; LIU et al., 2007).
According with Koops et al. (1997) N2O emission by urine applied in very dry
soil is mainly produced by nitrification, as an aerobic process. The maximum nitrification occurs with soil at 35-60% water content (KHALIL et al., 2004; BATEMAN; BAGGS, 2005) and NH4+is available in the soil.
In moist soil with 60% of water filled pore space (WFPS), denitrification is the predominant source of nitrous oxide emissions, due to N mineralization and hindered diffusion of O2 into the soil, favouring the formation of anaerobic environments
(MONAGHAN; BARRACLOUGH, 1993; PARTON et al., 1996; MERINO et al., 2001; BATEMAN; BAGGS, 2005). However, ambient with low O2 may occur naturally in
aerated soil like within an aggregate, where the diffusion of O2 is low. In the two
processes described, N2O is an intermediate product of soil microorganism’s
metabolism being released to the atmosphere.
value corresponds to the increase of reaction rate due to the increase in temperature of 10°C. For N2O emission, values reported in the literature vary between 2 to 10
(DOBBIE et al., 1999; SKIBA; SMITH, 2000).
Globally, livestock grazing is estimated to contribute with 1.5 Tg of N2O–N
release per year, which is more than 10% to the global annual N2O budget (KHALIL;
RASMUSSENR, 1992; OENEMA et al., 1997; 2005; IPCC, 2007). In a literature review, Oenema et al. (1997) estimated that between 0.1 and 3.8% of urine-N is emitted to the atmosphere as N2O.
2.3 The importance of livestock on greenhouse gas emission
In grazing system, carbon and nitrogen can be exchanged in many forms among atmosphere, plant, soil and animal. Sustainable pasture depends of nutrients balance to produce dry matter of sufficient nutritional quality for livestock (JARVIS, 2000). Recently, studies are focused on the impact of nutrient management on environmental quality and effects on air, soil and water composition.
The principle for livestock production is the conversion of plant protein to animal protein. Unfortunately, the conversion is inefficient, as for every 1 kg of high-quality animal protein produced, livestock consumed about 6 kg of plant protein is consumed (PIMENTEL; PIMENTEL, 2003). The inefficient conversion is a natural limitation, not dependent only of the grass management and quality but also animal genetic.
The production of high-quality animal protein depends of the availability of nitrogen, which is determined by the balance among inputs of biological N2 fixation,
anthropogenic sources and atmospheric N deposition, the recycling of plant residues and losses in gaseous (N2O and N2), inorganic (NO3- and NH4+) and dissolved
organic matter forms (VITOUSEK et al., 2002).
Losses of carbon and nitrogen in gaseous form are the most important contributor for greenhouse gases emissions from grazing system, and consequently to climate change through CH4and N2O emissions. The emission rates are related to
the management adopted in the production system as a whole. The most important gas is CH4 derived from cattle´s enteric fermentation, which represent about 22% of
The emission of N2O is mainly related to the deposition of urine on the soil by
animals, and also to fertilization with mineral N of pastures, thereby stimulating bacterial activity that produces nitrous oxide (W ILLIAMS et al., 1999).
Uneven deposition of excretal N by grazing animals can result in ´hotspots’
equivalent to an application of 400-2000 kg N ha-1 year-1 in the small affected area (W ATSON; FOY, 2001), leading to wide spatial and magnitude variations in N2O
emissions. These ´hotspots´ correspond to 14.5% of 1 ha during one year, considering a patch area of 0.4 m2per urine deposition (HAYNES; W ILLIAMS, 1993). In general with cattle, the proportion of the excretal N occurring in the urine increases from about 45% when the diet contains 1.5% N on dry matter basis to about 80% when the diet contains 4.0% N. Urea generally accounts for between 60 and 90% of the total N in the urine (BRISTOW et al., 1992; LANTINGA et al., 1987). Urine includes, in addition to urea, a number of other nitrogenous compounds, mainly hippuric acid, allantoin, uric acid, xanthine, hypoxanthine, creatine and creatinine. The proportion of the total urinary N accounted for by these compounds varies considerable.
Extensive cattle breeding occupy approximately 48% of arable land in Brazil. It represents the largest commercial herd in the world, accounting in 2010 for 14% of global beef production, according to the United Nations Food and Agriculture Organization (FAO, 2013). The latest agricultural census released by the Brazilian Institute of Geography and Statistics (IBGE/PPM, 2011), indicates that Brazil has 212.8 millions of beef cattle head, or more than one head per person. The main beef production system (96%) is characterized by the use of a large territory with pasture management performed in a continuous manner (ANUALPEC, 2011). Most of the slaughtered animals (60%) for beef production are 4.5 years old steers, with an average weight of 450 kg (FERRAZ; FELICIO, 2010).
Agriculture and livestock are the major contribute for greenhouse gas emission in Brazil, promoting 476 Gg N2O emissions, representing 87% of the total N2O
emission. The urine deposition in soil by animals during grazing is the most important source of N2O emissions from agricultural soils in Brazil. These emissions contribute
with 48% of N2O on agriculture; it means 41% of total CO2-equivalent emissions
(BRASIL, 2010; CERRI et al., 2009).
steers (castrated bulls), heifers (young females) and young bulls. The calves can be from beef herds or dairy herds, depending of the rearing and finishing system. The complex mix accounts for the wide diversity in the quality and prices of beef products in the UK. This sector is recognized in the national inventory as being the largest single source of N2O (JACKSON et al., 2009) corresponding to more than 50% of
GHG emissions in CO2-equivalent basis. The N2O emissions represent 80% of total
emission, originated by fertilizer N applications, grazing (urine) returns and manure applications to land on agriculture according with UK GHG Emission Inventory 2007 (JACKSON et al., 2009). This inventory also assumes that grazing returns contribute with 4.3 Mt CO2-equivalent or 17% of total N2O emissions from UK agriculture. These
values had shown the importance to study the environmental impacts of this livestock activity in the world and build a GHG Emissions National Inventory.
2.4 Potential mitigation: the nitrification inhibitors
In grazing production systems, most of the NO3- leached and N2O-N emitted
are derived from the N deposited particularly by animal urine (DI; CAMERON, 2002; DI et al., 2007).
One of the new technologies that has been shown to be effective to decrease both NO3-leaching and N2O emissions is the use of a nitrification inhibitor (NI) to treat
grazed pasture soils (e.g. ABBASI; ADAMS, 2000; DI et al., 2007; ZAMAN et al., 2009; SAGGAR et al., 2009; AKIYAMA et al., 2010). In recent years, numerous compounds, chemical, agents or materials have been identified and used as NIs. The application to the soil temporarily delays the bacterial oxidation of the NH4+ to nitrite
by inhibiting Nitrosomonas spp. (ZERULLA et al., 2001). The prerequisite for denitrification is the presence of a source of nitrate; in view of this, the application of nitrification inhibitor can minimize the N2O emission from denitrification as well as
from the nitrification process. Both processes are main responsible for N2O emission
on the soil.
environmental sustainability and advance the efficiency of mineral N cycles within soil, plant and animal systems (DI; CAMERON, 2003, 2005).
DCD is naturally broken down in the soil into nontoxic products, with no traces of residue left beyond the cropping year (AMBERGER, 1989). Also, it is easy to blend with fertilizers due to minimally volatile nature (CAMERON; DI, 2002).
It has also some disadvantages as a slightly more expensive for large-scale use in agriculture. Its action is comparatively weak, so high application rates are needed for effective nitrification inhibition. Additionally, under certain agroclimatological conditions, DCD use may cause phytotoxic problems like visible plant damage (MACADAM et al., 2003), which, although not leading to reduced yields, affects marketability of leaf vegetables.
Many experiments have been testing the DCD application directly on urine patch in pastures. These studies shows high efficacy of DCD in reducing N leaching and N2O emissions (DI; CAMERON 2007; MONAGHAN, 2009). However, it is
difficult to apply DCD on commercial pastoral farms because there is no technology available to precisely apply only on urine patch and the application over the whole farm has not been economically efficient.
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3 NITROUS OXIDE EMISSIONS FROM SOIL DUE TO URINE DEPOSITION BY GRAZING CATTLE IN BRAZIL
Abstract
Urine deposition to the soil can result in nitrous oxide emissions through the microbial processes of nitrification and denitrification. The objective of this experiment was to estimate N2O emissions from urine depositions in summer to grassland in Southeast
Brazil. In order to achieve the objective, a field experiment was conducted in which N2O emission from known volumes of urine applied to the soil were measured using
the static chamber method. Measurements continued for one month after application. Application of urine to soil increased N2O fluxes compared to those from the control
site. There were two significant N2O emission peaks for the urine treatment, between
days 2 and 9. The N2O emissions accounted for 0.2% of the urine N, lower than the
current IPCC default emission factor of 2% of N excretion for grazing cattle. The information obtained from this research will be useful as a contribution to the scientific basis for developing inventories of GHG emissions with different levels of complexity (Business, Regional or National) for extensive cattle production of cattle.
3.1 Introduction
One of the most important current environmental issues is the increase in global warming caused by greenhouse gas (GHG) emissions. Nitrous oxide (N2O) is a
potent greenhouse gas for which agriculture is a major source, with a global warming potential 298 times that of carbon dioxide (FORSTER et al., 2007).
In grazing livestock systems, urine patches contribute significantly to anthropogenic emissions, with nitrogen (N) deposition rates of between 500-1000 kg ha-1 to the soil (HAYNES; W ILLIAMS, 1993). The urea content of cattle urine will readily hydrolyze to form ammonium after deposition to the soil. Nitrous oxide may then be emitted through the microbiological processes of nitrification and denitrification, which are affected by soil and climatic factors such as soil enzyme activities, nitrate concentrations, pH, available carbon, rainfall/irrigation, water-filled pore space and temperature (BOLAN et al., 2004; LUO et al., 2008).
The Intergovernmental Panel on Climate Change (IPCC, 2006) gives a default N2O emission factor from cattle urine of 2%, i.e. 2% of the urine nitrogen is assumed
to be emitted as N2O-N. However, there is large uncertainty in this emission factor
and different countries and regions must have different specific N2O emission factors
due to different soil, temperature, rainfall and grazing systems, among others. In addition, the emission factor may be quite different for urine and faecal depositions
(IPCC doesn’t differentiate); it is generally assumed that emissions are greater from
the urine N which is in a more readily available form than the faecal N (e.g. YAMULKI et al., 1998; LUO et al., 2009). To improve national inventories of GHG emissions, and as a first step to developing mitigation strategies for this source, it is necessary to develop specific emission factors for the systems and conditions relative to the specific country.
In order to estimate total N2O emissions from urine deposition by grazing cattle,
it is necessary to know the numbers of animals, the specific N2O emission factor as
concentration to estimate total urine volume. According with Borsook and Dubnoff (1947), creatinine is synthesized in the muscles and is excreted in the urine steadily in relation to body weight. This urine volume estimate obtained from spot sample is based on a constant creatinine excretion for a given body mass and it is not influenced with animal dietary, as described by Palmer et al. (1914), cited by rskov e Macleod (1982). Thus, once it is possible to estimate the daily creatinine excretion from animal's body weight, the daily urine volume can be estimated from the creatinine concentration in a urine sample collected from spot sample, and then it will be possible to estimate the urinary volume.
The aim of this experiment was to provide the first data for Brazil relating to N2O
emissions from urine deposition by grazing cattle. Specifically, to measure N2O
emissions from urine applied to pasture in the summer in the Southeast region of Brazil.
3.2 Material and Methods
3.2.1 Experimental site
The experiment was carried out on a permanent grassland, from 31 January to
29 February of 2012 (summer) at Escola Superior de Agricultura “Luiz de Queiroz”
(ESALQ), Piracicaba, São Paulo state, Brazil (22º 42´07´´S; 47º 37´17´´W , 530 m above sea level) under tropical climatic conditions (K˚ppen climatic classification). The soil was a sandy loam classified as Nitisol (FAO, W RB). Soil properties (upper 10 cm) at the start of the experiment were: total N of 0.29%, total C of 3.03%, organic matter of 35 g dm-3, pH of 5.6 and bulk density of 1.13 Mg m-3. The pasture was not grazed by livestock before or during the experiment and had not received any N fertilizer for five months prior to the experiment.
3.2.2 Urine characteristics
In order to estimate the daily urine production, a spot sampling technique was used to assess the excretion of creatinine. Spot samples were collected (totalling 20 L) and sub-samples of 10 mL of urine were taken and diluted with 40 mL of a solution of 0.036 mmol L-1H2SO4and stored at −20°C for later analysis of creatinine.
This compound of the purine derivates was determined by a colorimetric system with end point reaction, using picrate and an acidifier, using commercial kits (555-A Sigma Chemical Co., St. Louis, MO).
From the measured creatinine concentration in the spot sample and the estimated daily average creatinine excretion according with equation from Chizzotti et al. (2004), the daily urine volume can be estimated divided measured creatinine concentration by estimated creatinine. From analysis of the spot samples, total N and ammonium N concentrations of the urine were 5.5 g L-1 and 12 mg L-1, respectively. Urine total volume was estimated using a creatinine analysis as 10.5 L steer-1day-1, agreeing well with estimates of 10.9 - 11.1 L day-1 given by Silva (2001). From observations of the animal behaviour over a period of 15 days, an average of 10 urination events per day was estimated, agreeing well with observations by Orr et al. (2012) and Whitehead (1995). A typical urination event for a given steer would therefore constitute a volume of approximately 1L urine. This was the volume of urine used in this experiment to simulate a single urine patch.
3.2.3 Nitrous oxide measurement
Nitrous oxide fluxes were determined using the static chamber method (BOW DEN et al., 1990). Chambers (0.064 m2) were randomly distributed across the field with a minimum distance of 5 m from each other. Chambers either received 1L of urine (urine treatment) or no urine (control treatment), with 5 replicates for each treatment. The application of urine was carried out on the first day of the experiment, less than half-hour before the beginning of sampling.
and 85°C. The N2O concentration was determined using an electron capture detector
(ECD). Gas fluxes were calculated by fitting linear regressions through the data collected at t_0, t_5, t_10 and t_20 and were corrected for temperature and barometric pressure according to ideal gas law from Eq. (1):
Eq. (1)
Where: = N2O flux (mg m-2h-1); = density of N2O (mg m-3); = volume of chamber (m3); = base area of chamber (m2); = average rate of change of concentration wit time (ppmv h-1) and = temperature in the chamber (°C).
Gas sampling was conducted every three hours after the treatment application on the first day and then daily during the first week of the experiment, and twice a week until the last day of the experiment. Cumulative N2O flux was calculated by
linear interpolation of the average N2O emissions between the measurements and
summing the results over the total time period.
Meteorological data (rainfall and air temperature) were recorded at the nearest meteorological station, which was within 1 km of the field site. The air temperature inside and outside the chamber was measured at each site and used to correct the concentrations of N2O inside the chamber as described above.
3.2.4 Derivation of an emission factor
An emission factor (EF) was calculated according to Eq. (2), by using the arithmetic mean per treatment of the accumulated N2O emissions over the
experimental time.
3.2.5 Statistical analysis
Data were verified for normal distribution and treatment means for daily N2O
fluxes and cumulative flux over the period of the experiment were compared using one-way analysis of variance (GenStat, VSN International). To determine the statistical significance of the mean differences, Tukey tests were carried out at 0.05 probability level.
3.3 Results and discussion
3.3.1 Climatic conditions and nitrous oxide emissions
The air temperature ranged from 22 to 28°C (Figure 1a). The daily soil temperature ranged from 15 to 26°C (Figure 1b), although it was above 21°C for more than 75% of the time. There were two peak rainfall events between 10-22 days after urine application, with a maximum daily rainfall of 49.8 mm on day 11 (Figure 1c).
There was an immediate step increase of N2O emission from the soil after urine
application compared to the control treatment (Figure 1d). There were two significant N2O emission peaks for the urine treatment, between days 0 and 9 with a maximum
emission rate of 1250.25 (± 336.7) µg N2O-N m-2 h-1, and between days 10 and 18
with a maximum emission rate of 863.32 (± 414.4) µg N2O-N m-2 h-1. After that,
emission from the urine treatment was not significantly different from the control (P>0.05) (Figure 1d). The highest peak N2O emission was on the 3rdday, very shortly
after the urine application when the soil temperature was 24ºC. The second peak coincided with rainfall events at 10-15 days after urine application. The higher N2O
emissions are related with higher standard error. It often occurs when we study the gases emissions; the emissions variability is common as found in many studies (UCHIDA et al., 2011; DOBBIE; SMITH, 2001; LUO et al., 2008; ZAMAN; NGUYEN, 2012). However, it can be observed that these peaks corresponding with statistical difference between control and urine treatments.
The measured N2O emissions had a temporal variation between around 100 to
900 µg N2O-N m-2h-1, dependent especially on climatic conditions. Previous studies
The first peak in our study is comparable with other studies. Maljanen et al. (2007) reported a maximum emission rate of 1200 µg N2O–N m-2 h-1, while de Klein
et al. (2003) recorded maximum emission rate of 300 to 4900 µg N2O–N m-2 h-1 from
cattle urine applied to grass. Ma et al. (2006) and Lin et al. (2009) reported peak rates of 1426 and 1707 µg N2O–N m-2 h-1from sheep and yak urine, respectively. In
New Zealand, in studies on silt loam soil with clover-based pasture, Luo et al. (2008) reported higher N2O emissions from the soil after cow urine application compared
with those from our study, with emission peaks between days 1 and 21. The emission observed immediately after urine application may be as a result of nitrification, due to the increase in ammonium nitrogen levels in the soil.
The first peak was about one and half times higher than the second. For the second peak, we can assume that denitrification was the predominant process leading to N2O emissions due to the rainfall increasing the soil water content. Soil
Figure 1 - (a) mean daily air temperature in °C; (b) mean daily soil temperature measured at 5 cm in °C; (c) daily rainfall in mm; (d) N2O emission from the soil following urine application on summer season. Vertical bars show ±1 standard error (n=5). Piracicaba-SP, Brazil. 2012.
0 5 10 15 20 25 30 m e a n d a ily a ir te m p e ra tu re ( ° C ) 0 20 40 60 R a in fa ll (m m ) 0 5 10 15 20 25 30 m e a n d a ily s o il te m p e ra tu re ( ° C ) 0 400 800 1200 1600
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 N2 O f lu x ( u g N 2 O -N m -2 h -1)
days af ter urine application
control urine a)
d) b)
3.3.2 Nitrous oxide emission factor
The cumulative N2O-N emission from urine application was higher than the
control, with a net emission of 0.17 g N2O-N m-2 after 30 days of the experiment.
Following the Eq. (2), with 85 g N-input m-2 was found 0.20% of N2O EF from the
summer experiment in Brazil.
Using this EF, an emission per animal can be derived using typical country values for urination rates and urine nitrogen content, which can be expressed as CO2
equivalents. Using collected information (typical values for steers from grazing system in Southeast Brazil) as: urination per day = 10.5 L day-1; nitrogen in urine = 5.5 g L-1, was found 0.11 g N2O-N animal-1day-1; that can be expressed as 51.5 g
CO2equivalent animal-1day-1.
The current IPCC default inventory EF for N deposition by grazing cattle is 2% (IPCC, 2006). In our study we found a much lower EF (0.2%). Luo et al. (2008) reported EFs for urine applications in New Zealand of between 0.02 and 1.59%, depending on the season.
This variability in reported EFs highlights the importance to determine specific EFs for each country or climatic region. The results from this study represent some of the first data for Brazil, but are limited in terms of duration (one month only), spatial representation (one site only) and seasonal representation (summer only). Extrapolating these results to regional or national emissions is therefore not appropriate. In addition, when expressing the EF per animal, the diet and level of productivity of the animal are also important factors to consider. To develop regional or national EF, many other studies are necessary to taking into account the range of soil, climate and management conditions within a country.
3.4 Conclusions
Application of steer urine to the soil increased N2O emissions during the
summer season in Southeast Brazil. Emission rates fell to background within one month after application. The N2O emission factor for cattle urine was 0.20% of the
cattle. This was equivalent to 0.0515 kg CO2-eq animal-1 day-1. More research is
needed in order to determine robust emission factors for the different regions of Brazil.
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